Tlc p01 network_services_2012

University of Roma
“La Sapienza”

Telecomunicazioni
Docente: Andrea Baiocchi
DIET - Stanza 35, 1° piano palazzina “P. Piga”
Sede Facoltà S. Pietro in Vincoli
E-mail: andrea.baiocchi@uniroma1.it

Corso di Laurea in Ingegneria Gestionale
A.A. 2011/2012

2

Programma
1. SERVIZI E RETI DI TELECOMUNICAZIONE (KR-
Cap. 1; GW-Cap. 1)
2. FONDAMENTI DI COMUNICAZIONI
3. ARCHITETTURE DI COMUNICAZIONE
4. SERVIZI DI RETE E MODI DI TRASFERIMENTO
5. STRATO DI COLLEGAMENTO E ACCESSO
MULTIPLO
6. TECNOLOGIE DI STRATO DI COLLEGAMENTO
7. LO STRATO DI RETE IN INTERNET
8. LO STRATO DI TRASPORTO IN INTERNET
9. CENNI SUI PROTOCOLLI APPLICATIVI
Telecomunicazioni - a.a. 2011/2012 - Prof. Andrea Baiocchi

Communication Networks and
Services

Basic terminology and concepts

4

The big picture
Users

Communication
Communication
Network
Network

Users run applications and interact via a
communication network

5

Applications
• Client-server
– Few host (servers) have got information content,
processing power or any needed facility and are ready to
answer to service requests from a much larger number of
hosts (clients)

• Peer-to-peer
– Many hosts (peers) cooperate to create service, with
possibly small help from some centralized servers

• Also:
– Uni/bi-directional
– Interactive or not


6

Examples: client-server apps
• Email
• FTP
• SSH, Telnet
• WWW
• E-commerce
• Audio & video streaming
• Web 2.0


7

Examples: p2p apps
• Telephony, Voice/Telephony-over-Internet
• Instant messaging: messenger, SMS
• File sharing: eMule, BitTorrent,…
• Real-time P2P: Skype, IPTV
• Network interactive games


8

What is a communication network?

Communication
Network

• The equipment (hardware & software) and facilities
that provide the basic communication service
• Virtually invisible to the user; represented by a
cloud

• Equipment • Facilities
– Routers, servers, – Copper wires, coaxial
switches, multiplexers, cables, optical fiber, radio
hubs, modems, …
– Ducts, conduits,
telephone poles …

9

Analogies
• A communication network provides services
– This is like utilities, e.g. water supply, electric supply,…

• Flexible connectivity
– This is like transportation systems

Goods / people

information


Approaches to long-distance
10

communications
• Transfer of messages made up of
– parseable sequence of symbols (digital information)
– continuously variable physical quantities (analog
information)
• Courier: physical transport of the message
– Messenger pigeons, pony express, FedEx,…
• Messages can be transferred by means of
transmission and reception of signals
– Drums, beacons, mirrors, smoke, flags, semaphores,…
– Electromagnetic field
• We focus on electrical communications


11

Example of digital communications
• Morse code converts text message into sequence
of dots and dashes
• Use transmission system designed to convey dots
and dashes
Morse Morse Morse Morse
Code Code Code Code

A ! — J !——— S !!! 2 !!———
B —!!! K —!— T — 3 !!!——
C —!—! L !—!! U !!— 4 !!!!—
D —!! M —— V !!!— 5 !!!!!
E ! N —! W !—— 6 —!!!!

F !!—! O ——— X —!!— 7 ——!!!
G ——! P !——! Y —!—— 8 ———!!

H !!!! Q ——!— Z ——!! 9 ————!
I !! R !—! 1 !———— 0 —————


12

Digital Transmission Evolution

Wavelength
Division
1.0E+14 Multiplexing
Information transfer

1.0E+12
per second

1.0E+10

1.0E+08
SONET
1.0E+06 T-1 Carrier Optical
1.0E+04 Carrier
Baudot
1.0E+02

1.0E+00
1850 1875 1900 1925 1950 1975 2000

Morse


13

Multiplexing
• Point-to-point communication systems:
– tx + communication link + rx

• Usually much more capacity available than
useful/affordable for single user pair
• Natural approach: put multiple information flows
of different user pairs onto the same shared
communication system
• Generalizable to point-to-multipoint
communications


14

The N2 Problem
• For N users to be fully 1
connected directly
– Requires N(N – 1)/2
connections, i.e. scales N 2
with square of number of
users
..
.
– Requires too much
communication resources,
4 3
often underutilized:
inefficient & costly

• Basic idea to improve:
resource sharing N = 1000
N(N – 1)/2 = 499500


15

Switching
• Since information flows share same link, there is a
need of intermediate dispatching
– Analogous to railway or bus stations

• A system where more links converge (input) and
from which more links depart (output) is defined
as a switching node if it has the task of deciding
and actuating the correct output for each piece of
information coming from an input
– In Internet context known as router;
– in telephone circtui networks known as exchange;
– in LAN or ATM contexts known as switch.


16

Switching: telephony example
• Patchcord panel switch invented in 1877
• Operators connect users on demand
– Establish circuit to allow electrical current to flow from
inlet to outlet

• Only N connections required to central office

N 1

N–1

2
3


17

A Circuit switching A3

0 0 0 0
1 1 1 1
2

2
31 62 62 31
A1 A2

B B3
B1 B2
C1 C2

0 0 0 0
0
1 1 1 1
1

61 C2
31 62 62 31
62

C C3

0 0 0 0
1 1 1 1

61 31
31 62 62 31


18

Hierarchical Network Structure
Toll
CO = central office

Tandem

Tandem CO
CO
CO
CO CO

Telephone subscribers connected to local CO (central office)
Tandem & Toll switches connect COs

19

Packet switching

Input
lines 1

2
Routing Output
lines
3
Store&Forward


20

Communications modes
• With connection
– Two or more parties
– Stateful
– Three phases: Set up, Data transfer, Tear down

• Connectionless
– Two or more parties
– Stateless
– Single phase: Data transfer


Example: telephone call
1. Telephone Pick up phone
network

Dial tone.
2. Telephone
network
Connection
set up Dial number
3. Telephone
network

Network selects route;
4. Telephone Sets up connection;
network
Called party alerted

Information
transfer 5. Telephone
network Exchange voice
signals

Connection
6. Telephone
release network Hang up.

22

Communication Network Architecture

• Network architecture: the plan that specifies
how the network is built and operated
– Architecture is driven by network services and relies
on available technology

• Overall communication process is complex:
therefore network architecture partitions overall
communication process into separate functional
areas called layers
– E.g. physical layer, end-to-end layer,…


23

Architecture layer view
• Given a layer of the network architecture, the
communication network can be modeled by a graph
– Vertices are nodes that cooperate with neighboring nodes to
support upper layer service
– Edges define (logical) direct communication links used by
nodes to cooperate

• Network topology

• Interface (node-to-node)

• Protocol (layer)


24

Network topology
• Refers to a given
architecture layer view
of the system
• Specifies connectivity,
i.e. capability of direct
interaction between
peer entities
• Topology model: a
graph


Connections of all Internet
25

sub-networks in the world


26

What is an interface?
• Contact point between two entities at a given level of
abstraction (layer)
– In the graph model of the layer, an edge between two nodes
corresponds to an interface
• Entity: piece of sw/hw able to perform a task by co-
operating with other remote, peer entities
• An interface is defined by specification of the
following aspects:
– Mechanical (only for physical interfaces)
– Electrical (only for physical interfaces)
– Functional (role played by any part of the interface)
– Procedural (sequence of events that involve one or more
functions of the i/f: protocol)


27

Example: ITU-T V.24
Linea
Interfaccia telefonica Interfaccia
47.17 DTE/DCE commutata DTE/DCE
mm DTE DCE DCE DTE
(Terminale) (Modem) (Modem) (Terminale)
13 12 11 10 9 8 7 6 5 4 3 2 1
Composizione
numero Cifre di DTR ON
25 24 23 22 21 20 19 18 17 16 15 14 telefonico selezione
RI ON

RTS ON
CD ON

Instaurazione
Tono

Fase di
Modalità Audio
Breve
Dati
DTR ON Ritardo

DTE DCE !
DSR ON
Toni Audio
CTS ON

(Dati) TxD
RxD
22 Ring Indication
RI RTS OFF
20 Data Terminal Ready
CD OFF
DTR

trasferimento dati
RTS ON Toni Audio CTS OFF
8 (OFF)
CD Carrier Detect

Fase di
7
SIG Signal Ground Breve
6 Ritardo
DSR Data Set Ready
5 CTS ON
CTS Clear To Send ! TxD
Toni Audio
(Dati)
4 RxD
RTS Request To Send
3
RxD Receive Data Toni Audio

abbattimento
RTS OFF (OFF) RTS OFF
2

Fase di
TxD Transmit Data CTS OFF CTS OFF
1 Shield Ground
SHG CD OFF CD OFF

Connettore 25 pin
ISO 2110
! Spia luminosa accesa Spia luminosa spenta


28

Example: Ethernet

• Specification of electrical quantities (current, voltage) and
waveforms (sync pulse trains, pulse shape)
• Specification of access procedures: Medium Access Control (MAC)
protocol


29

What’s a protocol?
a human protocol and a computer network protocol:

Hi
TCP connection
request
Hi
TCP connection
Got the response
time? Get http://net.infocom.uniroma1.it
2:00
<file>
time


30

Protocol elements
• A protocol is a set of rules that governs how two or
more parties communicating over an interface are
to interact
• Examples
– Internet Protocol (IP), Transmission Control Protocol
(TCP), HyperText Transfer Protocol (HTTP), Simple Mail
Transfer Protocol (SMTP)

• Key elements of a protocol
– Syntax
– Semanthics
– Timing

31

Protocols
• A protocol can be described by means of state
machines
• State is the set of variables whose value is
sufficient to decide next transition given input and
internal events
– E.g. message receipts, timer expiration
• Given state at time t, X(t)=a, any event occurring
in the interface at a subsequent time t+h makes
the state evolve to b
• Actions are associated to transition a->b.

Protocols define format, order of msgs sent and received
among network entities, and actions taken on msg send/rcv

Services

Internet at large

33

Packet Switching
• Internet is but one example of a packet switched
network
• Basic ideas:
– Information is segmented into “small”, self-contained
chunks (smaller than typical amount of information to be
transferred) -> PACKETS
– Packets hop from one node to another until they find their
way to the destination -> STORE & FORWARD
– Hop can be realized by ANY underlying communication
technology -> INTERNETWORKING
– Improvement of QoS demanded to end-to-end protocols
(e.g. error recovery, flow/congestion control)


34

High-level view of Internet
• Hosts, routers and inter-networking

H

H
Net 3
G
Net 1
G
G
G
Net 5
Net 2 Net 4
H G G
H


35

First packet switching ideas
Paul Baran, 1964


36

A closer look at network structure:
• network edge
– applications and hosts

• access networks
– wired/wireless
communication links
– large number of “small”
routers

• network core
– interconnected routers
– network of networks


37

Access networks
Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks wireless
xDSL - Digital Subscriber Line laptops

Dialup modem
to/from
modem router/
CO
firewall
wireless
access
point


38

Access networks
Q: How to connect end systems to edge router?
• residential access nets
• institutional access networks (school, company)
• mobile access networks
Wireless
LAN - Local Area Network
router

base
station

mobile
hosts


39

Internet structure: network of networks
• roughly hierarchical
• at center: “tier-1” ISPs (e.g., Verizon, Sprint, AT&T, Cable
and Wireless), national/international coverage
– treat each other as equals

Tier-1
providers
Tier 1 ISP
interconnect
(peer)
privately
Tier 1 ISP Tier 1 ISP


40

Tier-1 ISP: e.g., Sprint

POP: point-of-presence

to/from backbone

peering
… …
.
…
…

…

to/from customers


41

• “Tier-2” ISPs: smaller (often regional) ISPs
– Connect to one or more tier-1 ISPs, possibly other tier-2 ISPs

Tier-2 ISPs
Tier-2 ISP pays Tier-2 ISP also peer
Tier-2 ISP privately with
tier-1 ISP for
connectivity to Tier 1 ISP each other.
rest of Internet
! tier-2 ISP is
customer of
tier-1 provider Tier 1 ISP Tier 1 ISP Tier-2 ISP

Tier-2 ISP Tier-2 ISP


42

• “Tier-3” ISPs and local ISPs
– last hop (“access”) network (closest to end systems)

local
ISP Tier 3 local
local local
ISP ISP
ISP ISP
Local and tier- Tier-2 ISP Tier-2 ISP
3 ISPs are
customers of Tier 1 ISP
higher tier
ISPs
connecting
them to rest Tier 1 ISP
of Internet
Tier 1 ISP Tier-2 ISP
local
ISP
local local local
ISP ISP ISP

43

• a packet passes through many networks!

local
ISP Tier 3 local
local local
ISP ISP
ISP ISP

Tier 1 ISP

Tier 1 ISP Tier 1 ISP Tier-2 ISP
local
ISP
local local local
ISP ISP ISP

44

Hourglass model (H. Schulzrinne)


Services

Outlook

46

Trends in Network Evolution
• It’s all about services
– Building networks involves huge investment
– Services that generate revenues drive the network
architecture
• Current trends and issues
– Multimedia applications
– Info-centric communications
– End of trust
– Legal issues (laws are local, network is global)
– Overlay networks
– Nano-networks
– E-government, e-business, e-commerce

47

Declination on Internet
• Internet of Communities: organization of people activities
through the Internet, on the basis of common interests and
likings.
• Internet of Services: interconnection of providers and
consumers of any type of service that can be accessed
through the Internet.
• Internet of Media: network supporting media search,
delivery, and integration, regardless their format, providing
suitable storage and quick access.
• Internet of Things: pervasive network, capable of
connecting all devices that can generate, transmit, or receive
contents, including sensors, cameras, wearable devices.


48

Evolution of services
Yesterday, …today,
call switching… call center


49

Network models:
intelligent vs dumb

Source: M. Dècina, 2006


50

Network models: flat
• Mesh, ad hoc networks
– IEEE 802.11 e 802.16

• Pervasive and
ubiquitous computing
– Domotics,
embedded/wearable
computing
– event-driven, context-
aware, communicating,
networked smart objects

• Wireless sensor
networks
– ZigBee, RFID Source: M. Dècina, 2006


51

End of Trust
• Security Attacks
– Spam, Phishing, Pharming
– Denial of Service, DDoS
– Viruses
– Impersonators
• Firewalls & Filtering
– Control flow of traffic/data from/to Internet
• Confidentiality, integrity and authentication;
authorization; traffic monitoring
• Anonymity, privacy


52

ICT security attributes


53

TCP/IP stack & security


54

Operations, Administration,
Maintenance, and Billing
• Communication like transportation networks
– Traffic flows need to be monitored and controlled, QoS
and security must be guaranteed, possibly at different
levels
– Tolls have to be collected
– Roads have to be maintained
– Need to forecast traffic and plan network growth
• Highly-developed in telephone network
– Entire organizations address OAM & Billing
– Becoming automated for flexibility & reduced cost
• Under development for IP networks


55

Success Factors for New Services
• Technology not only factor in success of a new
service
• Three factors considered in new telecom services

New
Market Service Technology
Can there be Can it be
demand for the implemented cost-
service? effectively?

Regulation
Is the service
allowed/somehow
constrained?

56

Role of regulation
• Public regulation is fundamental as communication
services become a commodity
• Minimum service access to be guaranteed
– Universal service

• Digital divide
• Also fundamental for
– unique resources (radio spectrum)
– protection of public interests (e.g. health)


57

Standards
• New technologies very costly and risky
• Standards allow players to share risk and benefits
of a new market
– Reduced cost of entry
– Interoperability and network effect
– Compete on innovation
– Completing the value chain
• Chips, systems, equipment vendors, service providers

• Example
– 802.11 wireless LAN products


58

Standards Bodies
• Internet Engineering Task Force (IETF)
– Internet standards development
– Request for Comments (RFCs): www.ietf.org
• International Telecommunications Union (ITU)
– International telecom standards
• International Standardization Organization (ISO)
• IEEE 802 Committee
– Local area and metropolitan area network standards
• Regional bodies (ETSI, ANSI)
• Industry Organizations and Fora
– 3GPP, MPLS Forum, WiFi Alliance, World Wide Web Consortium,
Bluetooth


Services

History

60

Computer Network Evolution Overview
• 1950s: Telegraph technology adapted to computers
• 1960s: Dumb terminals access shared host computer
– SABRE airline reservation system
• 1970s & 1980s: Computers connect directly to each other
– ARPANET packet switching network
– TCP/IP based internetworking
– Ethernet local area network
• 1990s & 2000s: New applications and Internet growth
– Commercialization of Internet
– E-mail, file transfer, web, P2P, streaming . . .
– Internet traffic surpasses voice traffic


61

Internet History (1/5)
1961-1972: Early packet-switching principles
• 1961: Kleinrock - queueing theory shows effectiveness of
packet-switching
• 1964: Baran - packet-switching in military nets
• 1967: ARPAnet conceived by Advanced Research Projects
Agency
• 1969: first ARPAnet node operational
• 1972:
– ARPAnet public demonstration
– NCP (Network Control Protocol) first host-host protocol
– first e-mail program
– ARPAnet has 15 nodes


62

ARPANET - September 1971


63

1972-1980: Internetworking, new and proprietary nets
• 1970: ALOHAnet satellite network in Hawaii
• 1974: Cerf and Kahn - architecture for interconnecting nets
• 1976: Ethernet at Xerox PARC
• Late 70’s: proprietary architectures: DECnet, SNA, XNA
• Late 70’s: switching fixed length packets (ATM precursor)
• 1979: ARPAnet has 200 nodes

Cerf and Kahn’s internetworking principles:
– minimalism, autonomy - no internal changes required to interconnect nets
– best effort service model
– stateless routers
– decentralized control


64

1980-1990: new protocols, a proliferation of networks

• 1983: deployment of TCP/IP
• 1982: smtp e-mail protocol defined
• 1983: DNS defined for name-to-IP-address translation
• 1985: ftp protocol defined
• 1988: TCP congestion control
• new national networks: Csnet, BITnet, NSFnet, Minitel
• 100,000 hosts connected to confederation of networks


65

1990, 2000’s: commercialization, the Web, new apps
• Early 1990’s: ARPAnet decommissioned
• 1991: NSF lifts restrictions on commercial use of NSFnet
(decommissioned, 1995)
• Early 1990s: Web
– hypertext [Bush 1945, Nelson 1960’s]
– HTML, HTTP: Berners-Lee, 1989
– 1993: Mosaic, later Netscape
• Late 1990’s
– commercialization of the Web
– network security to forefront
– estimated 50 million host, 100 million+ users
– backbone links running at Gbps


66

• 2000’s
– more killer apps:
• instant messaging
• P2P applications (BitTorrent - file sharing; Skype - VoIP;
PPLive - video)
• YouTube
• Gaming
• E-commerce
– wireless, mobility
– tens/hundreds Gbps backbone


67

The Internet gotha


68

Internet statistics
• ~769 million hosts (July 2010)
• ~2 billion users
• As of Feb. 27rd, 2012: 138,143,921 Top Level Domains
• As of Feb. 1st, 2012: 3,479,770,880 IP addresses assigned in 246
countries
End of 2009:
• 234 million websites
• 247 billion emails sent daily on the average
• Facebook serves 260 billion page views per month (6 millions per
min)
• YouTube serves 1 billion videos per day


69

Host count


Tlc p01 network_services_2012

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